FIELD OF THE INVENTION
This invention relates to treatment of sewage and more particularly, to the treatment of sewage by aeration using a cylindrical treatment tank with a specially designed system of perforated air drop lines which eliminates the requirement of a conventional deflector located at the bottom of the treatment tank and extending into the small, open end of an inverted, cone-shaped clarifier. A unique air drop line design which includes linearly-spaced drop line openings for diffusing air from the drop lines into the aeration zone or chamber of the treatment tank in an optimum manner, faciliates withdrawal of effluent of extremely high quality from the quiet or quiescent zone at the flared, open top of the clarifier. In a preferred embodiment of the invention the spaced drop line openings face each other and the clarifier and are designed to minimize the coalescence of air bubbles and optimize contact of the bubbled air with the bacteria-laden effluent in the aeration zone, to optimize the quality of the effluent removed from the top of the clarifier in the quiescent zone.
Conventional sewage treatment systems normally include a sewage treatment tank of selected design, which tank is generally constructed of a cylindrical outer mixing tank and a center-located, invented funnel settling chamber called a clarifier. Raw, unsettled waste water and solid waste from a residence or business enters the aeration chamber of the mixing tank, which is located between the tank wall and the clarifier, where simple hydraulic displacement is accomplished by the introduction of air that promotes the growth of aerobic organisms in much larger colonies than would occur naturally. These organisms break down the organic solids in the waste water, producing inorganic and stable organic solids. Air is normally introduced into these tanks through vertical drop lines to effect the desired aeration and this aeration provides dissolved oxygen in the effluent, mixing of the waste water and sufficient time for the organisms or bacteria to break down the organic solids that have entered the treatment plant. From the mixing tank aeration chamber, mixed liquid enters the cone-shaped settling chamber, or clarifier, from a small opening in the bottom. No mixing occurs in this quiet or quiescent zone, where solids separate from the liquid, settle through the opening in the bottom of the clarifier, re-enter the mixing chamber and collect on the bottom of the treatment tank. The liquid that separates from the solids in the clarifier continues to flow hydraulically upwardly to the effluent discharge pipe. This liquid is typically a clear, odorless effluent discharge which meets or exceeds state water quality standards, and the objective of all sewage treatment systems is to produce an effluent having a desirable suspended solids content, biological oxygen demand (BOD) and dissolve oxygen (DO) content. When a new system is installed, it is typically located below ground at a sufficient elevation that will facilitate the necessary fall to effect a gravity flow of sewage from the home or business into the tank. A compressor is placed above ground in a suitable housing or enclosure for supplying air to the air distribution system and the air pumped from the compressor is typically bubbled through the effluent from the open-ended air drop lines in the treatment tank. The tank is initially filled with clear water and is then ready for operation.
It is an object of this invention to provide a new and improved sewage treatment system which utilizes multiple air drop lines of unique perforated design to effect an optimum biological balance in the treatment tank and an effluent of exceptionally good quality which is pumped from the treatment tank for disposal.
Another object of this invention is to provide a sewage treatment system which includes a cylindrical treatment tank that does not need or contain a deflector plate or solids deflection system and instead, incorporates plugged and perforated air drop lines of unique design, which perforations are characterized by multiple, linearly-spaced openings facing the clarifier to facilitate optimum distribution of air into the turbulent zone or aeration chamber of the treatment tank and promote oxygenation of the water, optimize the growth of bacteria and produce an effluent of exceptionally good quality at the top of the clarifier.
Still another object of this invention is to provide a new and improved sewage treatment system that uses a treatment tank having a cylindrical wall fitted with four drop lines plugged at the ends and equally spaced around the tank circumference and having multiple, linearly-spaced air discharge openings facing the clarifier, which air discharge openings are located above the level of the small, open end of the clarifier to eliminate the need for a conventional deflector plate in the treatment tank and optimize the dissolved oxygen (DO) content, biological oxygen demand (BOD) and suspended solids of the water pumped or flowing from the clarifier.
A still further object of the invention is to provide a sewage treatment system which is characterized by a cylindrical, sub-surface treatment tank having four downwardly-extending air drop lines connected to an air distribution system, each of which drop lines is characterized by a plug in the bottom end and five air openings provided on one-inch linear centers, for introducing air into the turbulent or aeration zone or chamber of the treatment tank between the tank wall and the clarifier, at an optimum rate and bubble distribution to optimize the dissolved oxygen content of the water in the tank, faciliate handling a wide variety of organic loading and achieve an optimum biological balance in the treatment tank.